Self-drilling anchor with enlarged bore zone



M- 16, 1969 F. CHROMY 3,467,209

SELFDRILLING ANCHOR WITH ENLARGED BORE ZONE Filed July 12, 1966 F191 5 3 PRIOR ART C V a? )4 lb 1/ (24 p/ 2 g ATTORNEYS United States Patent Int. Cl. E21c 13/08; EiMb 1/48; E21b 9/];

US. Cl. 175-395 Claims ABSTRACT OF THE DISCLOSURE A self-drilling anchor includes a tubular body having a central bore divided into a mounting zone, at one end, an axially relatively short core bit zone at the opposite end and a relatively elongated zone intermediate the mounting and core bit zones. The body has cutting surfaces at the outer end of the core bit zone which terminate radially at the external periphery of the body. The bore inner diameter in the core bit zone is less than that of the zone immediately adjacent thereto whereby to provide for easy flow of drilling debris from the core bit zone and through the tubular body. The mounting zone is preferably internally threaded for mounting of the self-drilling anchor on a percussion-type tool. Preferably, the exterior surface of the tubular body is formed with spiral grooves opening into an annular groove just inwardly of the cutting surfaces, providing for easy flow of drilling debris along the exterior surface of the tubular body. Alternatively, the exterior surface of the tubular body, inwardly of the cutting surfaces, may be formed with a series of axially spaced annular grooves.

Background of the invention Conventional anchors of this type usually have a continuous bore extending throughout the length thereof with a screwthread cut into its rearward section which extends approximately over half the axial length of the anchor. The diameter of the smooth bore extending forwardly from the threaded section is uniform throughout. The core bit at the forward end of an anchor of this kind is usually provided with two different tooth formations of generally triangular shape and disposed adjacent to each other. The different tooth forms have the same radial wall thickness at the base which corresponds to the wall thickness of the anchor. However, the sides of the teeth converge to a point disposed on the outer periphery of the anchor wall. The alternate teeth of one group are provided with an inwardly-directed chamfer from the apex to facilitate axial alignment when the usual locking cone is inserted, even while the anchor is driven in. When the anchor is being driven into a hard receiving material the degree of chamfer is increased due to abrasion.

When the anchor is driven a condition arises in which the core bit and end of the anchor acts on the receiving material over an annular area of greater width than the thickness of the wall of the bit. The material removed by the rotary impact motion of the anchor is the confined within the cavity formed by its axial bore. In other words, an increasing amount of material consisting of drillings and boring dust, is compacted Within the bore of the anchor to form a dense plug of the material. An actual discharge of the drillings is possible only when the plug of material reaches the screwthreaded part of the bore or after the anchor has been driven into the receiving material a distance equal to one-half its length at which time the compacted drillings expand into the space where the cross-section is increased by virtue of the screwthreads cut into the smooth bore. Thereafter, the drillings are discharged upwards from the anchor.

The compacting of the drillings in the smooth zone of the anchor bore increasingly obstructs the transfer and entry of the newly cut material into the bore so that part of this material tends to be discharged between the outside wall of the anchor and the wall of the borehole. The presence of such cuttings in the space between the bore-hole and the anchor is apt to cause the anchor to jam in the hole, thus extending the drilling time and making more difficult the removal of the anchor after the completed drilling operation.

Summary of the invention This invention relates to a self-drilling anchor having a central bore and a core bit at one end.

The object of the present invention is to provide an improved self drilling anchor which avoids the above described disadvantages of anchors of conventional construction.

According to the present invention the section of the bore at the zone where the mouth of the core bit merges into the adjacent smooth section ha a smaller diameter than the diameter of the aforementioned smooth section. As a result of this construction, the cuttings are compacted in the bore for only a short distance before they enter the larger section where they may expand so as to produce a continuous and uniform discharge of the cuttings. The short plug of material forming in the front zone of the anchor is not sufliciently compacted to prevent material cut at the bottom of the bore-hole from entering into the anchor bore. Thus, the structure eliminates excessive flow of cuttings between the bore-hole wall and the excessive flow of cuttings between the bore-hole wall and the external wall of the anchor together with any accompanying jamming of the anchor in the bore-hole.

Also, the axial length of the core bit zone of smaller diameter as measured from the bit end preferably corresponds with or is less than the bore diameter. We have also deter-mined that it is possible to achieve excellent re sults with such anchors when the length of the core bit section having the smallest diameter is less than the diameter of the anchor bore. A particularly advantageous construction of the anchor from a production standpoint is obtained if the diameter of the smooth zone of the bore adjacent to the core bit zone corresponds to the inside diameter of the screwthread zone, which, as already mentioned, is usually larger in conventional core bit anchor constructions.

An additionally improved discharge of the boring dust cut at the external circumference of the anchor can be obtained by providing the external wall of the anchor with helical groves for the automatic discharge of such boring dust and for the reduction of the jamming length relative to the bore-hole. The spiral grooves merge into a circular groove disposed in the outer periphery of the anchor adjacent the teeth of the core bit zone. For manufacturing convenience it is possible to provide, instead of helical grooves, only circular grooves which also reduce the jamming area of the anchor in the bore-hole.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a section through an anchor of conventional construction to show the state of the prior art;

FIGURE 2 is a plan view of the anchor shown in FIGURE 1 and showing the teeth of the bit;

FIGURE 3 is a section through an anchor incorporating the novel features of the present invention;

FIGURE 4 is a side elevational view on a reduced scale of an anchor of modified construction having helical groves on its outer periphery; and

FIGURE is a view similar to FIGURE 4 of another modified construction having circular grooves on its outer periphery.

An anchor of conventional construction as known in the prior art is shown in FIGURES 1 and 2 and has a continuous bore 1 of a diameter 1a extending longitudinally through the zones c and b. The rearward zone a, has an internally threaded section 2 which extends approximately one half the axial length of the body of the anchor. The threaded section 2 usually has an inner diameter 1b which is slightly larger than the diameter 1a. A coupling projection 3 is provided to enable the anchor to be secured in a percussion drilling apparatus (not shown) and which, on completion of a driving operation, is separated from the actual anchor body. The continuous bore in the part b of the anchor extends through the core bit which has by teeth 4, of triangular shape and cut into the front end of the anchor, to form an annular cutting edge.

As can also be seen from FIGURE 2, the teeth 4 are usually so constructed that teeth 4 have a radial dimension corresponding to the wall thickness of the anchor and are adjacent to and alternate with intermediate teeth 4 which correspond to the wall thickness in the radial direction only at the base of the tooth. These later teeth taper outwardly from the base to zero wall thickness at the tip at the external circumference of the anchor body. To facilitate centering of the locking cone (not shown), the inner faces of the tips of the teeth 4 are each provided with an inwardly-converging chamfer 5.

In accordance with the present invention, the anchor as shown in FIGURE 3 is provided with a bore of a diameter 1a for a short length in the zone 0 at the bit end. In other words, the bore of the anchor at bit zone c has a diameter 1a which is less than the diameter 1b of the bore adjacent the zone c. This difference in diameters results in an expansion of the bore into which the cuttings may flow after leaving the core bit zone c. In the illustrated embodiment and by comparison with FIGURES 1 and 3, it will be seen that the reduction of the diameter in the zone c relative to the zone b is produced by counterboring the zone b to the same diameter as the inner diameter 1b of the internal screwthreaded section 2 in the zone (1. Variations are, of course, also possible with respect to the diameter differences between a and b and the relation between the length of core bit end section 0 and its diameter In. Good results were obtained with a diameter difierence of the bores 1a and 1b of between 0.5 mm. and 1 mm., the dimension 0 of the core bit end corresponding approximately to the diameter 1b. The dimension 0 may also be smaller than the diameter 1a or 1b.

In the embodiment of anchor shown in FIGURE 4 an improved construction is provided for the discharge of the drilling dust occurring at the external circumference of the anchor. This improved construction comprises helical groves 9 cut in the external wall of the anchor and the grooves extend into a circular circumferential groove 10 adjacent the core bit zone. The drilling dust initially collects in the grooves 10 and is then automatically conveyed along the grooves 9 by the rotating and/ or vibrating motion resulting from the percussion 6 effect of the percussion drilling apparatus. In addition, removal of the anchor is facilitated in that the grooves 9 effect a subdivision of the jamming area of the anchor relative to the bore-hole and reduce the overall frictionalsurface. The reduction of the frictional surface is also achieved in the case of the anchor according to FIGURE 5 in which the outer peripheral surface of the anchor is provided with circular grooves instead of helical grooves, thus simplifying the manufacture of .the anchor.

What we claim is:

1. A self-drilling anchor comprising a relatively elongated tubular body having a central bore divided into a mounting zone at one end, an axially relatively short core bit zone, at the opposite end, and a relatively elongated zone intermediate said mounting and core bit zone; said body having cuting surfaces at the outer end of said core bit zone terminating radially at the outer periphery of said body; the bore internal diameter in said core bit zone being less than that of the intermediate zone, said intermediate zone being immediately adjacent said core bit zone and merging thereinto.

2. A self-drilling anchor as claimed in claim 1, characterized in that the axial length of the core bit zone is no greater than the internal diameter of said adjacent bore section.

3. A self-drilling anchor as claimed in claim 1, characterized in that the axial length of the core bit zone is less than the internal diameter of said adjacent bore section.

4. A self-drilling anchor, as claimed in claim 1, in which said mounting zone has an internal screw thread, the internal diameter of said intermediate zone being equal to the internal diameter of said screw threads.

5. A self-drilling anchor comprising a relatively elongated tubular body having a central bore divided into a mounting zone, at one end of thebody, a core bit zone, at the opposite end of the body, and a relatively elongated zone intermediate said mounting and core bit zones; said body having cuting surfaces at the axially outer end of said core bit zone terminating radially at the external periphery of said body; said body being formed with grooves in its otherwise substantially uniform diameter external surface, said grooves reducing the area of the external surface of said body relative to the surface of the bore-hole in which jamming may occur; said groves being formed throughout the axial extent of the external surface of said tubular body from a point immediately inwardly axially of said cutting surfaces to the axially outer end of said mounting zone, said groves including a circular grove disposed adjacent to the core bit zone and spiral groves having one end extending into said circular groove.

References Cited UNITED STATES PATENTS Re. 23,539 8/1952 Tilden 175-403 X 730,786 6/1903 Murphy 175-414 2,856,157 10/1958 Chapin et a1 175403 X 2,998,086 8/1961 Demo 175-405 X 3,202,035 8/ 1965 Rosselct 175-405 X 1,467,451 9/1923 Phillips 175-405 FOREIGN PATENTS 20,849 1889 Great Britain. 1,023,768 3/1966 Great Britain.

208,432 4/ 1909 Germany.

CHARLES E. OCONNELL, Primary Examiner IAN A. CALVERT, Assistant Examiner US. Cl. X.R. -68; -405 

